Conference Agenda

<p>Geonet-geocomposites are a common replacement for granular drainage layers, providing drainage, venting, and capillary separation for controlling water content in soils, and controlling hydraulic head around buried structures. They can also contribute to the reduction of the carbon footprint of the project, while reducing or even avoiding the use of quality granular materials, which are getting scarcer and scarcer in many regions of the world.</p>

<p>First developed as biplanar structures during the 80’s, geonets have evolved toward a variety of structures, including triplanar, triaxial and box-shaped geocomposites. Early designs were mostly focusing on achieving a high flow capacity of the drainage core. Over time and with a better understanding of the behavior of these products, better-performing structures were developed. Products were also developed to provide efficient solutions to specific problems such as the drainage of coal combustion residues, or the recirculation of leachates in bioreactors, among others.</p>

<p>This paper describes the various structures used for manufacturing geonet-geocomposites. Mechanisms influencing the long-term compressive properties and flow rate are described, such as ribs roll-over, structural contribution of transversal ribs and tensile modulus of the geotextile.</p>

<p>The capacity of different types of geonets to resist sustained stress is quantified using laboratory tests covering aspects such as creep and geotextile intrusion. Results are explained in the context of recent normative developments, i.e., in ISO TC221 and ASTM D35.</p>

<p>The results of an ongoing study on the long-term behaviour of a PVC-P geomembrane installed on the upstream face of masonry and concrete dams are presented. In the last 30 years, since dams rehabilitation with this type of geosynthetics, the exposed PVC-P geomembrane are sampled periodically and tested in laboratory. Material properties measured at the laboratory are compared with the ones obtained from test on virgin samples when available. The sampled geomembranes have been subjected to physical and mechanical tests and the results interpreted with reference to the variation of plasticizer, tensile characteristics, foldability at low temperatures, and volumic mass. In particular, the decrease in plasticizer content resulted in slightly higher modulus and tensile strength. The experimental program allowed the study of the evolution of the properties of the geomembrane over the years and therefore it has been possible to assess the residual life of exposed geomembranes installed on the upstream face of dams.</p>

<p>Coupled physical and hydraulic experiments are conducted to quantify leakage through circular geomembrane holes with diameters of 10 mm, 20 mm, and 50 mm. Three different tailings, fine-grained tailings with fines content of 90 % and <em>d</em>₁₀ of 1 µm (denoted as T1), silty sand tailings with fines content of 30 % and <em>d</em>₁₀ of 20 µm (denoted as T2), silty sand tailings with fines content of 20 % and <em>d</em>₁₀of 40 µm (denoted as T3), are examined. The effective stress and pore pressure in the tailings above geomembrane and remote from the hole are ~170 kPa and ~350 kPa, respectively. Test results show that leakage through geomembrane hole is proportional to the hole diameter (and not the area) for each type of tailings, and highly dependent on the fines content of the tailings. For example, the leakage for a T2 and T3 tailings are 1.8-fold and 65-fold greater than that for the T1 tailings, respectively, for a given hole size. The practical implications are discussed.</p>

<p>Geosynthetic barriers are widely used in sealing applications throughout the world.In applications with constant water heads, such as artifical ponds, rivers, canals, etc. the permeation rate through the barrier system, including the overlap areas influences the succes or failure of the barrier system. But not only the barrier performance is of importance, also the overlap performance (or the welding of the overlaps plays an important role, as well as the water head, the water surface and the evaporation. Factors which are sometimes underestimate or not considered.</p>

<p>This paper will introduce a calculation tool, which considers several of these influencing factors and was developed to compare several sealing systems with each oth - under the onsite conditions and calculate not only the permeation rates but also the influence of the shape of the structure and the evaporation based on different model approaches and summarize the methods and other influecing parameters.</p>

<p>A large part of embankment dams ensures their waterproofing function by a specific waterproofing device using a geomembrane, generally called geomembrane lining system (GLS). This is particularly the case with embankment dams of small to intermediate dimensions, such as high altitude reservoirs, intended for the production of artificial snow, almost all sealed by GLS, and a significant part of hill reservoirs intended for irrigation uses. For these structures, the GLS is essential because a failure of this component compromises the waterproofing of the dam and its mechanical stability.<br />During the operation phase, leaks may appear in the geomembrane by mechanical actions (puncturing, creeping of ice, etc.). To drain accidental leaks, drainage systems under the geomembrane provide a fundamental safety barrier preventing water from entering the backfill. In their design, drainage systems are often compartmentalized in order to detect leaks, but this technique can be improved and does not make it possible to precisely locate the leaks or to quantify them.<br />This article presents the development of an active optical fiber device to address the issue of leak detection, and to allow operators to monitor the performance and safety of their structures. The proposed monitoring system aims to develop simple and economical solutions by quickly and precisely locating the leaks to be repaired. The article gives recommendations for optimizing the heating of the fiber and the heating power, in relation to the measured leakage rates. After rapidly developing the methodology for interpreting the data, the article presents the results obtained which allow the location of the leak to be determined.<br />The development of the proposed device was carried out by INRAE with the company geophyConsult in a full-scale experimental basin available to INRAE at its Aix-en-Provence site. This project was supported under the RESBA project funded by Europe (ALCOTRA INTERREG program).</p>